[release-branch.go1.14] cmd/compile: don't short-circuit copies whose source is volatile
Current optimization: When we copy a->b and then b->c, we might as well
copy a->c instead of b->c (then b might be dead and go away).
*Except* if a is a volatile location (might be clobbered by a call).
In that case, we really do want to copy a immediately, because there
might be a call before we can do the a->c copy.
User calls can't happen in between, because the rule matches up the
memory states. But calls inserted for memory barriers, particularly
runtime.typedmemmove, can.
(I guess we could introduce a register-calling-convention version
of runtime.typedmemmove, but that seems a bigger change than this one.)
Fixes #43574
Change-Id: Ifa518bb1a6f3a8dd46c352d4fd54ea9713b3eb1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/282492
Trust: Keith Randall <khr@golang.org>
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
(cherry picked from commit 304f769ffc68e64244266b3aadbf91e6738c0064)
Reviewed-on: https://go-review.googlesource.com/c/go/+/282559
diff --git a/src/cmd/compile/internal/ssa/gen/generic.rules b/src/cmd/compile/internal/ssa/gen/generic.rules
index 87cfd3d..89368ed 100644
--- a/src/cmd/compile/internal/ssa/gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/gen/generic.rules
@@ -2351,7 +2351,7 @@
(Move {t1} [s] dst tmp1 midmem:(Move {t2} [s] tmp2 src _))
&& t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq
&& isSamePtr(tmp1, tmp2)
- && isStackPtr(src)
+ && isStackPtr(src) && !isVolatile(src)
&& disjoint(src, s, tmp2, s)
&& (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
-> (Move {t1} [s] dst src midmem)
@@ -2360,7 +2360,7 @@
(Move {t1} [s] dst tmp1 midmem:(VarDef (Move {t2} [s] tmp2 src _)))
&& t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq
&& isSamePtr(tmp1, tmp2)
- && isStackPtr(src)
+ && isStackPtr(src) && !isVolatile(src)
&& disjoint(src, s, tmp2, s)
&& (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
-> (Move {t1} [s] dst src midmem)
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index d65d900..72abaf2 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -32031,7 +32031,7 @@
return true
}
// match: (Move {t1} [s] dst tmp1 midmem:(Move {t2} [s] tmp2 src _))
- // cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
+ // cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
// result: (Move {t1} [s] dst src midmem)
for {
s := v.AuxInt
@@ -32047,7 +32047,7 @@
_ = midmem.Args[2]
tmp2 := midmem.Args[0]
src := midmem.Args[1]
- if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
+ if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
break
}
v.reset(OpMove)
@@ -32059,7 +32059,7 @@
return true
}
// match: (Move {t1} [s] dst tmp1 midmem:(VarDef (Move {t2} [s] tmp2 src _)))
- // cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
+ // cond: t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))
// result: (Move {t1} [s] dst src midmem)
for {
s := v.AuxInt
@@ -32079,7 +32079,7 @@
_ = midmem_0.Args[2]
tmp2 := midmem_0.Args[0]
src := midmem_0.Args[1]
- if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
+ if !(t1.(*types.Type).Compare(t2.(*types.Type)) == types.CMPeq && isSamePtr(tmp1, tmp2) && isStackPtr(src) && !isVolatile(src) && disjoint(src, s, tmp2, s) && (disjoint(src, s, dst, s) || isInlinableMemmove(dst, src, s, config))) {
break
}
v.reset(OpMove)
diff --git a/test/fixedbugs/issue43570.go b/test/fixedbugs/issue43570.go
new file mode 100644
index 0000000..d073fde
--- /dev/null
+++ b/test/fixedbugs/issue43570.go
@@ -0,0 +1,40 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "fmt"
+
+type T [8]*int
+
+//go:noinline
+func f(x int) T {
+ return T{}
+}
+
+//go:noinline
+func g(x int, t T) {
+ if t != (T{}) {
+ panic(fmt.Sprintf("bad: %v", t))
+ }
+}
+
+func main() {
+ const N = 10000
+ var q T
+ func() {
+ for i := 0; i < N; i++ {
+ q = f(0)
+ g(0, q)
+ sink = make([]byte, 1024)
+ }
+ }()
+ // Note that the closure is a trick to get the write to q to be a
+ // write to a pointer that is known to be non-nil and requires
+ // a write barrier.
+}
+
+var sink []byte
